(1) Field of the Invention
The present invention relates to a process for producing a mixture of polyols containing relatively higher molecular weight triglyceride based polyols and a relatively lower molecular weight linear polyols. More specifically, the invention is related to such polyols derived from bio-renewable resources such as vegetable oils.
(2) Description of the Related Art
Mixtures of polyols are commonly used in the manufacturing of polyurethane and polyester articles resulting from the reaction of liquid polyol mixtures and liquid isocyanates or carboxylates, respectively. Mixtures of primary hydroxyl terminated functional groups in polyols are desirable in commerce as they undergo rapid polymerization processes and their compositions greatly impact the physical properties of the polymeric articles. Commonly employed polyol mixtures consist of blends of low equivalent weight glycols such as ethylene glycol or 1,4 butanediol and primary hydroxyl terminated high molecular-weight polyether polyols. However, many such blends are incompatible fluids that tend to separate into layers on standing and thus, these blends should be constantly agitated to avoid a misformulation of the polymer because of the separation of components. Even more compounds in the blends to migrate into one of the phases and adversely impact the polymerization process. Recognition of this problem dictates that polyol blends containing low molecular weight polyols and high molecular weight polyols should be constantly agitated or alternatively a “chain extender” or a “solubilizer” should be employed.
A “chain extender” is disclosed by Graefe et al. in U.S. Pat. No. 3,929,730 issued Dec. 30, 1975 incorporated herein by reference in its entirety. This patent teaches the use of blends consisting of 1,4 butanediol with high molecular weight polyols having molecular weights of 2,000 or greater where a sufficient amount of phenylenediethanolamine is used as an extruder to render the mixture homogeneous. Similarly, a “solubilizer” derived from butylene glycol or propylene glycol is disclosed in U.S. Pat. No. 3,993,576 to Barron and is claimed to render the polyol mixture resistant to phase separations.
Olstowski and Nafziger in U.S. Pat. No. 4,282,387, issued Aug. 4, 1981, incorporated herein by reference in its entirety1, disclosed the preparation of a mixture of polyether polyols by reacting alkylene oxides with hydroxyl initiator compounds in the presence of catalysts of calcium, strontium, or barium salts of organic acids. Although such catalysts need not be removed before the resultant product is used in the preparation of polyurethanes, they are generally available in a mineral spirit solvent which further contains monoether glycols that act as initiators. Consequently, mono functional species with respect to the hydroxyl group are present in the mixture and if their concentration is too high, they distract from the properties of the polymers when they are intended for high performance applications. Alternatively, Yates et al. in U.S. Pat. No. 4,326,047 discloses a process for preparing similar polyols mixtures using these catalysts wherein the catalyst is first precipitated from the mineral spirits carrier and the glycol ether coupling agent. The resulting catalyst is solid and thus, it must be re-dissolved in the reaction medium for it to be effective. This extra step takes time and negatively affects the productivity of the reaction and the polydispersity of the product prepared.
The vast majority of polyols are obtained from different petrochemical processes and are considered virgin polyols. Examples of such polyols include those prepared from terephthaloyl radicals as described in U.S. Pat. No. 3,647,759 to Walker; U.S. Pat. No. 4,237,238 to DeGiuseppi et al.; and U.S. Pat. No. 4,346,229 to Derr et al. It has also been disclosed that polyols can be obtained by chemical recycling processes for PET bottles as described in U.S. Pat. No. 4,048,104 to Svoboda et al. whereby pieces of poly(ethylene terephthalate) that is obtained from the collection of PET bottles are used to manufacture diethylene glycol and terephthaloyl radicals.
There are several known processes to chemically modified vegetable oils and produce triglycerides containing hydroxyl functional groups. One (1) method to prepare polyols from various vegetable oils is described in Brazil Pedido PI (2002) Application: BR 2000-5479 20001016 by Calderon Velasco, Rodrigo. It is based on transesterification of the fatty acids in the triglycerides with a polyol such as glycerin, trimethylolpropane, pentaerythritol, sorbitol, amino-alcohols, glycols including ethylene glycol, propylene glycol, diethylene glycol, and neopentyl glycol. Other hydroxylated compounds such as pentaerytol, -methylglucoside or sucrose are also suitable. Unfortunately, premature degradation occurs by this process due to high temperatures (200-240° C.) and a relatively long period of time in the tranesterification reaction. Furthermore, the resulting product distribution contains only glycerides and no low molecular weights linear polyols.
Another method described in U.S. Pat. No. 6,433,121, to Petrovic is based on a consecutive two-step process involving epoxidation and then hydroxylation of vegetable oils with peroxyacid to yield polyol mixtures. According to this method, the epoxide rings are open or hydroxylated with polyfunctional alcohols to yield secondary alcohols. Although epoxidized soy oil is available commercially, the reactivity of this oil is low since only secondary alcohols are obtained and these are inherently less reactive than primary alcohols. Furthermore, several hydroxyl groups per fatty acid residue are obtained by this route (at least these fatty acids that contain more than one double bond). Consequently, multiple numbers of hydroxyl groups having varying reactivity are present, which tend to complicate subsequent reactions and can even lead to premature gelation. These polyols have also been shown to exhibit poor functionality and thus, they must be mixed with other high functionality polyols so that when polymerized, sufficient cross-linking is achieved.
Hydroformylation of vegetable oils offers another method to prepare polyols described by Guo et al. in the J. of Polym. and the Environ. 10: 49-52 (2002). According to this method, an aldehyde functional vegetable oil is first obtained, which is then hydrogenated to alcohols. Polyurethanes prepared from these polyols had different mechanical properties depending on the hydroformylation catalyst that was used. Thus, rigid materials at room temperature were obtained with a rhodium catalyst while a cobalt catalyzed hydroformylation led to rubbery materials.
An alternative method for preparing primary polyols is based on oxidizing an olefin having a carbonyl group with molecular oxygen followed by hydrolysis and reduction of the acetal (or ketal) to an alcohol is described by Takahara, J. et al. in WO Application Patent 2002049999 (2002). This method is much more complicated and must run at high pressure and thus, is not very economical.
Another method described by Austin et al. in U.S. Pat. No. 4,314,088 is based on an oxidation process of the olefinic compounds to yield polyols using an organic hydroperoxide in the presence of OsO4 and a NaBr co-catalyst. However, the use of toxic heavy metals requires careful operation and disposal protocols of the waste heavy metal residue, which render this method not very practical. Another oxidation process employs ozone to cleave and oxidize the double bonds in the vegetable oil and then reduce the decomposing ozonides to alcohols using NaBH4 or similar reducing agents. Although the oxidation and cleavage of the double bonds are fast and effective, the subsequent reduction process is costly and not very useful commercially.
It is apparent from the foregoing that although polyols derived from various starting materials by a variety of processes have been disclosed, they either exhibit low levels of compatibility or are not sufficiently reactive or are not useful in the polymerization of polyurethanes and polyesters. Moreover, all the polyol mixtures obtained from vegetable or animal oils without complete cleavage of the double bonds are composed of relatively high molecular weight glyceride derivatives whereby complete cleavage of the double bonds in these oils lead to an unstable polyol mixture.